This invention relates generally to a method and apparatus for producing a composite material and, more particularly, is directed to a method and apparatus for producing a composite material of a highly elastic nature.
Three-layer and other multi-layer composite materials are known in which the joining of the layers is generally effected by stitching, bonding, flame-bonding, high-frequency welding or the like. However, all of the above methods have proven disadvantageous for one reason or another. For example, one disadvantage of stitching is that holes are made in the material so that water-tight products cannot be made therefrom. A disadvantage of bonding is that a solvent is required which must be evaporated by the application of heat thereto. Furthermore, in the case of flame-bonding of a foam, the foam must be heated to a temperature above its melting point, which requires a considerable amount of heat and causes dangerous gases to be produced. These gases must be eliminated according to laws generally governing the protection of the environment and this elimination can be done only at great expense. High-frequency welding can, as a rule, be effected only discontinuously. However, one serious disadvantage of the high-frequency method is that only a few materials can be welded together, namely, ones that have a suitable dielectric loss angle tan .delta., for example, non-rigid PVC with a tan .delta. equal to about 0.1 at a frequency of 10.sup.6 Hz, in contradistinction to polyethylene with a tan .delta. equal to about 0.0005 at the same frequency, the latter of which cannot be welded by the high-frequency method. Plastic coated metals can also not be welded by the high-frequency method.
Furthermore, it is known to produce composite materials having an upper layer, a lower layer, and a non-woven web as an intermediate layer by an ultrasonic spot welding method. However, a prerequisite for the manufacture of such composite materials has been that the materials of all three layers have the same or similar vibration properties so that they can be welded by ultrasonic frequencies. In practice, this requirement greatly limits the opportunity to use this method. For example, it is not possible with this method to join two outer layers of synthetic textile materials, which are capable of oscillation, with intermediate layers of a plastic foam, such as thick layers of polyurethane or polyethylene, synthetic rubber, or non-woven webs of wool, cotton, cellulose derivations, materials which have been impregnated or provided with a water-resistant finish, metals, paper, or the like. Also, a problem with such composite materials having intermediate layers of non-woven webs is that such composite materials are only slightly elastic since the non-woven materials therein are, as a general rule, inelastic or only slightly elastic.
It is therefore desirable to obtain, in an inexpensive and simple manner, composite materials having multidirectional elasticity and having an upper layer and an ultrasonically joined lower layer and an intermediate layer of any desired material without the necessity of making holes in the outer layers, as in the case of stitching, and without having to externally heat the materials, as in the case of welding.
It has been proposed in my copending U.S. patent application Ser. No. 06/105,295 to produce composite materials which have an upper layer, a lower layer secured to the upper layer along substantially parallel, spaced apart, ultrasonic weld seams, and an intermediate layer comprised of individual strands of material which lie substantially parallel to the weld seams between the latter in channels formed by the upper and lower layers. In the aforementioned copending application, the method therein is carried out with an apparatus comprised of a vibration or oscillating body used for ultrasonic welding, anvil plates which are spaced apart from each other in a parallel relationship, and guides for guiding the strands of material of the intermediate layer along with the upper layer and lower layer between the spaced apart anvil plates and the oscillating body.
Although the method and apparatus described in the aforementioned application results in a composite material of an elastic nature, it is desirable to provide still greater elasticity in the composite material and to be able to control the amount of elasticity therein.